Retrievable pilot operated gas lift valve



April 23, 1963 c. B. cHrrwooD 3,086,593

v RETRIEVABLE PILOT OPERATED GAS LIFT VALVE April 23, 1963 c. B. cHlTwooD 3,086,593

RETRIEVABLE PILOT OPERATED GAS LIFT VALVE Filed oct. 2, 1961 2 sheets-sheet 2 35 l INVENTOR.

i BY Q C 1mg? //c ATTORNEY United States Patent O M' 3,086,593 RETREEVABLE PILOT OPERATED GAS LIFT VALVE Charles B. Chitwood, Houston, Tex., assignor to Camco, Incorporated, Houston, Tex., a corporation of Texas Filed st. 2, 1961, Ser. No. 142,318 Claims. (Cl. 166-224) This invention relates to gas lift systems for producing well fluids and more particularly to an improved valving structure inclusive of a compact pressure responsive valve assembly especially adapted for retrievable mounting within a relatively small receiver pocket and through which pressure air or natural gas is introduced at selected depth into a well production tubing string.

An object of the invention is to provide a retrievable gas lift valve assembly having a longitudinal succession of operating components of minimal transverse dimensions housed within an elongated narrow chambered body with internal locating shoulders and co-operating securements for retainers Iby which replaceable main valve and pilotl valve seating rings are clamped in place and with external landing and releasable latching formations for abutment with mating formations of a valve positioning pocket in the tubing string.

A further object of the invention is to provide an improved valve assemibly for installation and removal from a tubing string section by wire line suspension equipment and provided with a self-actuated latch to effect positive anchorage in avalve receiver upon installation and an unlatching response to a pulling removal operation.

Another Object is to provide a valve assembly of improved design -to tit narrow tulbing space and to enable more economical manufacture and reliable operation with dependence on controlled lift gas pressures to cycle main n valve operation and quick action without the likelihood of flutter and seat pounding lin response to gas pressure imposed on the main valve through a direct acting pilot valve.

Other objects and advantages will appear from the following specification and the accompanying drawings in which FIG. l is a vertical sectional view of a fragment of a well installation showing la gas lift valve in an operative position in a well tubing string; FIGS. 2A and 2B are companion rviews partly in elevation and partly in vertical section of the improved valve structure anchored in its receiving pocket; FIGS. 3 and 4 are vertical sectional views of the lower portion of thel structure shown in FIG. 2B with latching dogs retracted and in the case of FIG. 3, near the end of the running-in operaltion, and in the case of FIG. 4, just after the start of a pulling operation, and FIG. 5 is a fragmentary vertical section showing a portion of the main valve on a scale somewhat larger than that of FIG. 2A.

Referring to the drawing, the usual well ybore lining or casing l1 has extended through it a production' tubing string 2 for the flow ofwell fluids from a producing formation to the wellhead. The tubing string includes one 0r more sections or special mandrels, such as shown at 3, Ifor the mountingv of pressure responsive valving by which lift gas is admitted into `the tubing string from the annular space within the casing 1.

yOpposite ends of the tubing section 3 are secured to adjacent ends of other tubing sections and an open passageway 4 joins the opposite ends in vertical alignment with the tubing string axis and is for the unobstructed passage of operating tools' through the valve carrying mandrel 3. Between its opposite ends, the mandrel 3 is enlarged in a direction laterally offset from the ma-in passageway 4 and encloses a tool receiving tubular pocket P which is longitudinally elongated and is located in a 3,086,593 Patented Apr. 23, 1963 region near the lower portion of the tubing section 3. Above this laterally offset pocket, the clearance spacing internally of the tubing section 3 accommodates manipulation of a kick-over wire line suspended device for the selective placement and removal of retrievable control devices into and from the oiset pocket. This tulbular pocket has its ibore opening at top and bottom Iinto the interior of the tubing section 3. At its upper end, the tubular pocket preferably has a downwardly tapered seat or landing shoulder 5 for a self centering action on an inserted tool, such as a gas lift valve assembly V, having a similarly tapered external shoulder. Near its lower end, the pocket has a downwardly facing and upwardly tapered seating shoulder y6 torprovide a latch keeper. Adjacent the end shoulders 5 and 6 and above and below an intermediate laterally relieved portion 7, the bore of the pocket `at 8 and 9 is carefully machined -to provide internal sealing and bearing surfaces for co-operation with mating sealing and bearing surfaces formed peripherally on an elongated valve body or other tool so that, except for the passage internally of the tool, 4the opposite ends of the pocket are sealed from the intermediate relieved portion 7 against the flow of gas admitted internally of Ithe pocket from the casing annulus and through one or more side entry ports =10 extending through the exterior wall of the intermediate portion of the pocket.

For use in controlling the admission of lift gas where space condition-s conne the size of a tool receiving pocket to a diameter of about one inch, transverse compactness has been `designed into a longitudinal succession of operating components. The resulting relatively narrow housing enclosure or valve body 11 is constituted by a vertical succession of tubular sections 11a, 11b, 11e, 11d, 11e, and 11]" and a top closure plug 11g terminating in an attachment head for connection with conventional wire line running and pulling devices. For convenience of manufacture and assembly, as well as later inspection and parts replacement, these several body sec- `tions are preformed separately and in `selected succession are screw threaded together in end to end relation.

The upper tubular body section 11j is formed with an external downwardly facing seat or shoulder 12 for stop abutment with the internal landin-g seat 5 of the tool receiving pocket. Peripherally surrounding an inwardly relieved lower portion of the body section 11f and clamped ybetween the shoulder thereon and the upper end of the body section 11e is a stack of V-shaped packing rings 13 Ifoi-'bearing sealing engagement with' the internal sealing surface 8 of the tool pocket. A similar stack of sealing rings 14 surrounds a lower relieved end of the body section 11C and is clamped in place by a'ring 15 carried on a locating shoulder near the upper end of the body section 11b. The packing rings 14 are for seal bearing engagement with the internal sealing surfaces of the pocket portion 9.

Below the clamp ring 15, the body section 11b has a peripheral twin spool formation with 'a pair of longitudinally extending annular relieved portions 16 `and 17 spaced or separated at adjacent ends from one another by an annular head or expander boss 18 Whose top shoulder is tapered upwardly for guiding and outward camming co-operation with the bottom internal corner of one or more spring fingers or legs 19 each having a terminal outwardly projected latching lug or dog 20 for co-operation with the latch keeper abutment 6 of the tool receiving pocket. As seen in FIG. 2B, the upper end of each laterally projecting dog 20 provides an upwardly facing abutment latch surface engageable with the downwardy facing shoulder or keeper abutment 6. By reason of such engagement, the dogs on the free ends of the lowermost body section 11a.

,.3 spring Vlegs constitute Vla'tching elements.- Preferably, the spring legs are designed to be straight longitudinally of the tool when the legs are unstre'ssed and hence they are yieldingly resistant to inward deilection at their free ends so that the latching dog terminal formations are outwardly biased in relation to the center line of the tool. As is best sh'own in FIGS. 2B and 3, the spring legs 19 are dependent longitudinally from and are integral with a retainer collar or ring 21 in sliding embracement with the upper relieved portion 16 and 4the length of the kportion 16 provides an over-all range of longitudinal slide collar travel between limits established by the underside of the clamp ring 15 and the upper face of the expander boss 18. Initially, such range of travel is restricted to a region immediately adjacent the ring 15 so that the inside faces of the spring fingers adjacent the latching lugs can move above the expander boss 18 for their lateral retraction into the relieved portion 16 and can move downwardly into laterally overlapping relation with the periphery of the expander boss 18 and which precludes retraction and maintains the latching lugs 20 outwardly expanded. Such initial lower limit is established by abutting engagement of the bottom edges of the spring legs 19 with a slide ring 22 releasably secured to the body section 11b by means of a shear pin or frangible connection 23. When the frangible connection is ineffective, ythe abutment ring 22 is free to drop downwardly to the bottom of the relieved portion 17 and .into stop abutment with the underlying terminal head of the body section 11a. This last mentioned relationship is illustrated in FIG. 4, which also shows the retaining ring 21 dropped to its lower limit in abutment with the expander boss 18 and with the bottom latching lugs 26 on the spring fingers depressed inwardly into the bottom relieved portion 17.

Near the upper end of this lower relieved portion 11b are one or more outlet ports 24 leading from the chambered body to the bottom opening of the tool receiving pocket. To prevent backflow into the valve charnber when tubing pressure exceeds casing pressure, a valve seat is formed internally vof the body section 11b above the outlet port 24 and with which co-operates an upwardly seating check valve 25 whose dependent guide stern is iitted within an upwardly extending skirt on the This upstanding skirt is radially spaced from the adjacent portion of the body section 11b and is provided -with a drain opening 26 at the lower end of the clearance and spaced some distance below the outlet ports 24. This arrangement tends to maintain the outlet ports 24 clear and free from the collection of debris.

For open communication to the interior of the valved body 11 from the annularly relieved portion 7 in the tool receiving pocket and from its inlet ports 10, there are provided a pair of longitudinally spaced apart sets of side inlet ports 27 and 28 leading respectively through the wall of the body section v11e to a pilot valve chamber and `through the wall of the body section 11d to a main ow valve chamber. Immediately below these inlet ports 27 and 28 are a downwardly facing shoulder 29 machined in the bore of the body section 11e and a downwardly facing shoulder 30 machined in the bore of the body section 11d. Located upwardly by the internal shoulder 29 and detachably held in place by a gland nut 31 screw threaded in the body section 111e is a replaceable annular valve seat or ring 32 for downward seating engagement by `the head 33 of a pilot valve assembly. Similarly, the internal shoulder 30 locates an annular valve seating ring 34 preferably of a somewhat pliable elastic deformable material and which is replaceably clamped in place by an apertured retainer ring 35 screw threadedly received within the bore of the body section 11d. As best seen in FIG. 5, the bottom internal corner of `the seating ring 34 is for line contact with an upwardly seated and tapered valve seat surface of the bottomhead 36 of a substantially spool-shaped main valve element 36a.

Extending upwardly from the lower valve head 36 is a reduced diameter stem portion 36b having terminal screw threaded connection with the upper head 37 of the spool valve which head has a sliding guide t within the counterbored cylindrical upper end of the body section 11d. The slidel bearing surfaces are sealed as by an O-ring 38 or the like carried by one or the other of one of the relatively slidable parts so iluid pressures active on top and bottom surfaces of the head 37 are confined. The shoulder 39 at the bottom of the cylindrical counterbore provides a stop abutment for the bottom of the head 37 to limit the main valve movement in the opening direction and against the upward bias of a coil spring 40 surrounding the stem and bearing at opposite ends on the head 37 and an internal shoulder on the body section 11b.

With the main valve closed against the seat ring 34, the radially grooved top face of the upper head 37 will be positioned with clearance above the head, with its entire area exposed to the central passages through the retainer ring 31 and valve seat ring 32. So long as the pilot valve 33 remains seated, iiuid pressure above and below the spool valve will be equalized by way of a vertical passage 41 extending longitudinally through the main valve, While the main injection valve is seated under bias of they spring 40, casing pressure supplied at the entry port 28 can act on the upwardly facing areas of the main valve as defined by the internal diameter of the seating ring 34 and on the downwardly `facing areas of the main valve as defined by the diameter of the cylinder in which the head 37 slides as decreased in each instance by the effective size of the head connecting stem. When these opposing surfaces are 'approximately :in balance, casing pressure thereon has no substantial effect on the action of the main valve. For some installations, these opposing surfaces may be made to present differential areas favorable for closing tendency in supplementing the elastic force of the coil spring 40 although, in any event, the coil spring will furnish the dominant closing force.

The downwardly biased pilot valve head 33 has its valve stem 44 joined to the free end of a flexible bellows seal 45 whose opposite or upper end is mounted on the body section 11g. Coniined within the interior of the bellows is a gas under pressure for furnishing an elastic downward Ibiasing force. The downwardly facing areas on the stem exteriorly of the bellows seal are exposed to casing pressure and control the opening and closing of the pilot valve. Bellows internal pressure is selected to maintain the pilot valve closed until casing pressure reaches a predetermined value. Unless that casing pressure is reached and exceeded, both valves remain seated. Until casing pressure has lifted the pilot valve 33 away from its seat to a degree that the pilot valve opening passes pressure fluid in an amount greater than can be vented through the main valve internal passage 41, the force of the main valve spring 40 plus any upwardly acting lift gas on differential `areas exposed thereto on the main valve, holds the main valve closed. Additional opening of the pilot valve as casing pressure increases for -a greater free passage of the pressure gas through the relatively large openings in the rings 31 and 32 results in pressure action directly against the upper face of the top head 37 of the main spool valve and the response will be a fairly rapid depression of and a iirm hold-open action on the main valve for large volume free flow of lift gas past the valve head 36. Elevation of production fluid through the tubing string will continue until casing pressure decreases below the bellows closing point, which reseats the pilot valve 33, whereupon a quick bleedoff of pressure through passage 41 from `above the upper head 37 allows upwardly biased closure of the main valve.

Ars seen in FIG. 2A, the lower valve head 36 has a screw threaded counterbored portion forming a continuation of the central passageway 41. This enables selective tment of a suit-able device eitherV to plug the central bore 41 orto choke the passage to any extent as determined by particular operating conditions.

In operative position, the valve assembly will be securely pocketed within the receiver, downwardly by reason of the external Ishoulder 12 and upwardly by reason of the expanded latching lugs 20. Upon downward insertion of a tool body within the receiver pocket, the lugs 20 will iirst come into engagement with the landing seat and will be stopped while the body continues downward and carries with it the expander boss 18 below the bottom of the momentarily arrested latchingv lugs. In the further body downward movement, the retainer ring 15 will fabut the mounting collar 21 and transfer the downward movement to the latch lugs 20 which ride inwardly on and are cammed by the shoulder or landing seat 5 into retracted relation within the upper body relieved portion 16 as -accommod'ated by inward deection of the exible spring legs 19. With such retraction, the lugs can pass through the restricted pocket portion 8` and then spring out into the annularly relieved intermediate portion 7 of the pocket.

They will again be similarly stopped and then retracted for passage through the pocket region 9, as illustrated in FIG. 3. Coincident with engagement with the land-ing seat 5 by the external body shoulder 12, the latching lugs 20 will have passed just belo-w the keeper shoulder 6 and will have sprung back and dropped down into abutment with the locating ring 22 and with their insides en- .gaged and in outwardly backed projected relation with the external annular surface of the expander boss 18. A downward jarring force will then release the running tool from connection with the top body section 11g for running tool removal.

For later removal of the retrievable unit, a wire line pulling tool will be caused to pick up the body by engagement with the top body portion 11g, whereupon an upward pull or jar transmitted to the body and resisted by latch engagement with the downwardly facing keeper shoulder 6 will eect breakage of the `shearable pin connection 23. Thereupon the stop ring 22 will drop out of blocking Irelation to the latching lugs 20 and elevation of the valve body will permit descent of the spring leg collar 21 to its lower limit, wherein the spring legs 19 position the terminal `latching lugs opposite the lower relieved body portion 17 for their retraction and inward bending of the legs in clearance relation to the 4keeper shoulder 6 and the reduced diameter bores of the pocket portions 9 and 8.

The foregoing description has dealt with the detail structure of the improved retrievable tool and lift gas control valving and is representative of the preferred but not necessarily the only embodiment and it is to be understood that such modications can be made as come within the scope of th-e appended claims.

What is claimed is:

1. In combination, a well tubing string section hav-v ing a passageway therethrough and a longitudinally extended tubular receiver offset laterally from and open at opposite ends into said passageway and provided with a gas lift entry port in the wall thereof and intermediate said ends, sealing surfaces formed internally of the receiver above and below said inlet port and adapted for co-operation with mating sealing surfaces on a well tool, an upwardly facing tool engageable seat on said receiver adjacent its upper end, a downwardly facing latch engageable seat on said receiver adjacent its lower end and a well tool'for latched reception within said receiver and including a body, a downwardly facing locating shoulder on the Ibody adjacent its upper end for engagment with the upwardly facing seat of the receiver, a laterally biased latch carried by the body adjacent its lower end and provided with an upwardly facing abutment to engage with said downwardly facing latch engageable seat, longitudinally spaced apart sealing surfaces peripherally carried by the body for bear-ing sealing engagement with th-e internal sealing surfaces of said receiver, a pair of longitudinally spaced apart annular valve seats positioned by the body internally thereof with the upper valve seat facing upwardly and the lower valve seat facing downwardly, flow outlet means in the body below said lower valve seat, means in the wall of the body communicating said lift -gas entry port with the interior of the body above each of said valve seats, a spoolshaped main valve member housed by the body. with the upper head end of the member slidably bearing on the body wall below said upper valve seat and with the lower head end of the member arranged for upward closing engagement with the lower and downwardly facing valve seat, spring means active on said member to bias the same upwardly, said member having a longitudinal ilow passage therethrough of lesser -ilow area than the flow area of the upper valve seat and a normally downwardly biased pilot valve housed by the lbody to seat on said upper seat and being responsive to given lift gas pressure above said upper seat to open for pressure gas action on the upper side of said upper head end of the spool-shaped member.

2. In combination, a well tubing string section having a longitudinally extending partition wall internally thereof affording a through passageway for well fluids and a tubular pocket for removable reception of a retrievable well tool, said pocket being open at both ends into the passageway and having a lift gas entry port intermediate said ends, internal bearing surfaces within said pocket and above and below the entry port for close seal fitment therewith of a well tool, a tool landing shoulder and a tool latch keeper on the pocket and a latchablev termediate portion thereof adjacent said `gas entry port,

longitudinally spaced apart peripheral bearing surfaces on the body above and below said intermediate portion of the body for mating sealing co-operation with the internal bearing surfaces of said pocket, a seating ring within the chambered body between said longitudinally spaced apart portions thereof, a pilot valve engageable with said ring, means biasing the valve toward ring engagement and responsive to the pressure of lift `gas to open said pilot valve pass pressure gas thereby, a valve seating ring below both of said longitudinally spaced portions of the chambered body, a longitudinally shiftable spool valve within the chambered body having its upper head end in peripheral sliding seal bearing with Vthe body and its top face exposed to pilot valve passed pressure gas and having its lower head end positioned for movement into and out of seating engagement with the last mentioned valve seating ring as influenced by pressure gas action on said upper headed end, spring means between the body and the spool valve normally maintaining the spool valve and its lower head in seating engagement with the last mentioned valve seating ring, a longitudinal passage through the spool valve, a body carried portion having a pair of longitudinally spaced apart peripheral grooves separated by an intermediate enlargement, a collar slidably fitted in one of the grooves and having a longitudinally extended spring leg with a lateral latching lug spaced from the collar for reception by said latch keeper, means dening opposite limits of collar movement in one of which said spring leg is depressible into one of said grooves and in another of which said leg is ldepressible into the other groove and means including a shearable connection on the body and precluding collar movement to one of said opposite limits and restricting collar movement with a range adjacent the upper limit and to and from the intermediate position in which said spring leg bears inwardly against said intermediate enlargement and is located thereby against depression.

3. In combination, a well tubing string section having a tool locating pocket with a lift gas entry port in the side of the pocket intermediate its top and bottom ends, internal cylindrical bearing surfaces in the pocket above and below said gas entry port, a tool landing shoulder on the pocket, a tool latch keeper on the pocket spaced longitudinally from the shoulder, a retrievable gas lift valve removably positionable in said pocket and comprised of a body enclosing a valve chamber and having medially of its length a side opening for communication of said entr; port with the valve chamber, a pressure responsive valve in the chamber controlling flow of lift gas, a pair of peripheral seals on the body on opposite sides of said side opening and engageable with said bearing surfaces in the pocket, a locating seat on the body for bottoming abutment with the landing shoulder, a keeper engageable latch dog mounted on the body for longitudinal and lateral shifting movement relative thereto, said -body in the region intermediate the range of longitudinal dog movement having a dog expander bossengageable by the dog for maintaining the same against lateral retraction from its latching position and also having portions above and below said boss which are inwardly relieved relative to the lboss and accommodate lateral retraction of the dog upon its longitudinal movement out of engagement with the boss and frangible stop means carried by the body below the dog engaging boss surface for engagement by the bottom of the dog and initially restricting dog longitudinal movement downwardly from the boss and into the relieved portion below said boss.

4. A retrievable well tool for removable reception within a tubing string pocket, including a body having a downwardly facing stop abutment and an upwardly facing stop abutment assembly which is self-latchable upon downward tool movement into a tubing string pocket and is releasable in response to upward jarring force applied to the tool, said assembly comprised of a spool formation onthe body having a pair oflongitudinally spaced apart peripherally relieved portions and an expander boss between said relieved portions, a longitudinally shiftable latching element having a retainer collar embracing the uppermost relieved portion and a dependent flexible leg having inward bearing abutment with said expander boss at an intermediate position of movement of the shiftable element and being inwardly retractable into said relieved portions at opposite limits of movement of said shiftable element, an outwardly projected latching dog carried by the flexible leg and a stop including an abutment portion and frangible positioning means therefor securing the abutment portion to the body in the downward path of said leg and engageable therewith to preclude -movement of the leg into the lowermost relieved portion lso long as said frangible positioning means is effective.

5. A retrievable gas lift valve assembly for removable reception within a tubing string pocket, including a chambered body, a downwardly facing locating shoulder external of the body, a latch mounting formation on the body comprising a pair of longitudinally spaced peripherally relieved portions and an expander boss separating the relieved portions, a self-acting latch comprising a retainer collar slidably sleeved on the upper relieved portion and provided with a downwardly extended spring leg carrying an upwardly facing latch lug on a portion of the leg spaced `below said collar and retractable into said relieved portions at opposite limits of collar slide travel and engaged with said boss against retraction at a collar position intermediate said opposite limits, body carried releasable means including a shearable connection and an abutment portion positioned by the shearable means on the body below said boss and engageable by the bottom of the spring leg as a stop against downward movement into the lower relieved portion, a spool-shaped main valve slidably mounted within the chambered body with an upper head in slide guide bearing on the body and with a lower head tapered upwardly to constitute a valve seating surface, an internal downwardly facing shoulder on said body immediately above the tapered seating surface, a pliable seating ring bearing on said shoulder and engageable by said tapered seating surface for closing the chambered body against lift gas flow, a retainer ring removably secured in the body in clamping engagement with said seating ring, spring means between the body and the main valve normally maintaining said main valve closed, a longitudinal passage through the main valve, a normally seated pilot valve -contained within the chambered -body above the main valve and responsive to lift gas ypressure in directing the same against the top of said upper head to depress the main valve, a downwardly facing shoulder internally of the body above said upper head, a pilot valve seating ring located upwardly by the last mentioned shoulder and a retainer ring removably mounted in the body in pilot valve seating ring clamping relation with the last mentioned shoulder.

References Cited in the file of this patent UNITED STATES PATENTS 2,846,014 Dafn et al. Aug. 5, 1958 2,869,645 `Chamberlain et al. Jan. 20, 1959 2,885,006 Long et al. May 5, 1959 2,994,280 Dain Aug. l, 1961 2,994,335 Dudley Aug. 1, 1961 

1. IN COMBINATION, A WELL TUBING STRING SECTION HAVING A PASSAGEWAY THERETHROUGH AND A LONGITUDINALLY EXTENDED TUBULAR RECEIVER OFFSET LATERALLY FROM AND OPEN AT OPPOSITE ENDS INTO SAID PASSAGEWAY AND PROVIDED WITH A GAS LIFT ENTRY PORT IN THE WALL THEREOF AND INTERMEDIATE SAID ENDS, SEALING SURFACES FORMED INTERNALLY OF THE RECEIVER ABOVE AND BELOW SAID INLET PORT AND ADAPTED FOR CO-OPERATION WITH MATING SEALING SURFACES ON A WELL TOOL, AN UPWARDLY FACING TOOL ENGAGEABLE SEAT ON SAID RECEIVER ADJACENT ITS UPPER END, A DOWNWARDLY FACING LATCH ENGAGEABLE SEAT ON SAID RECEIVER ADJACENT ITS LOWER END AND A WELL TOOL FOR LATCHED RECEPTION WITHIN SAID RECEIVER AND INCLUDING A BODY, A DOWNWARDLY FACING LOCATING SHOULDER ON THE BODY ADJACENT ITS UPPER END FOR ENGAGMENT WITH THE UPWARDLY FACING SEAT OF THE RECEIVER, A LATERALLY BIASED LATCH CARRIED BY THE BODY ADJACENT ITS LOWER END AND PROVIDED WITH AN UPWARDLY FACING ABUTMENT TO ENGAGE WITH SAID DOWNWARDLY FACING LATCH ENGAGEABLE SEAT, LONGITUDINALLY SPACED APART SEALING SURFACES PERIPHERALLY CARRIED BY THE BODY FOR BEARING SEALING ENGAGEMENT WITH THE INTERNAL SEALING SURFACES OF SAID RECEIVER, A PAIR OF LONGITUDINALLY SPACED APART ANNULAR VALVE SEATS POSITIONED BY THE BODY INTERNALLY THEREOF WITH THE UPPER VALVE SEAT FACING UPWARDLY AND THE LOWER VALVE SEAT FACING DOWNWARDLY, FLOW OUTLET MEANS IN THE BODY BELOW SAID LOWER VALVE SEAT, MEANS IN THE WALL OF THE BODY COMMUNICATING SAID LIFT GAS ENTRY PORT WITH THE INTERIOR OF THE BODY ABOVE EACH OF SAID VALVE SEATS, A SPOOLSHAPED MAIN VALVE MEMBER HOUSED BY THE BODY WITH THE UPPER HEAD END OF THE MEMBER SLIDABLY BEARING ON THE BODY WALL BELOW SAID UPPER VALVE SEAT AND WITH THE LOWER HEAD END OF THE MEMBER ARRANGED FOR UPWARD CLOSING ENGAGEMENT WITH THE LOWER AND DOWNWARDLY FACING VALVE SEAT, SPRING MEANS ACTIVE ON SAID MEMBER TO BIAS THE SAME UPWARDLY, SAID MEMBER HAVING A LONGITUDINAL FLOW PASSAGE THERETHROUGH OF LESSER FLOW AREA THAN THE FLOW AREA OF THE UPPER VALVE SEAT AND A NORMALLY DOWNWARDLY BIASED PILOT VALVE HOUSED BY THE BODY TO SEAT ON SAID UPPER SEAT AND BEING RESPONSIVE TO GIVEN LIFT GAS PRESSURE ABOVE SAID UPPER SEAT TO OPEN FOR PRESSURE GAS ACTION ON THE UPPER SIDE OF SAID UPPER HEAD END OF THE SPOOL-SHAPED MEMBER. 